1. Field of the Invention
The present invention relates to die heads for extruded filaments and particularly die heads for extruding meltblown fabrics.
2. Discussion of the Related Art
A general overview of meltblown polymer filament technology may be had by referring to U.S. Pat. No. 3,825,380 (Harding et al.).
Generally a single deep polymer-distribution channel is formed in the die head and multiple capillaries are drilled in the so-called xe2x80x9cknife edgexe2x80x9d, or extrusion edge of the die tip to contact the distribution channel and provide the extrusion channels and orifices for the fine, or small, diameter, meltblown fibers. The reader is also referred to U.S. Pat. No. 4,486,161 (Middleton) and U.S. Pat. No. 4,013,816 (Sabee et al.).
The words xe2x80x9cfibersxe2x80x9d and xe2x80x9cfilamentsxe2x80x9d will be used interchangeably in this specification.
However, owning to physical constraints of the die head, such as the requirement for a fine edge at the point of extrusion, there have always been tradeoffs between extrusion pressure and meltblown die capillary density in the meltblown die head. Ideally the maker of meltblown fabrics would prefer to have options for utilizing both higher pressures and greater capillary density than were previously available from prior art designs.
In order to accomplish the object of higher die head pressures and greater capillary, or extrusion orifice, density in a meltblown fiber die head, the present invention provides a die head with bores communicating with a central polymer distribution channel and running in the extrusion direction to communicate with multiple capillaries. At least some, or all, of the bores will have multiple capillary extrusion outlets. By distributing multiple capillaries to a bore, more metal may be retained in the die head thereby allowing higher pressures in the extrusion process while permitting higher capillary density.
It is anticipated that the die tip of the present invention will withstand extrusion pressures that would cause other seals in the die head assembly to fail, resulting in no practical pressure limit on the die tip of the present invention.